1. Field of the Invention
The present invention concerns hydraulic receivers, for clutch control, notably in motor vehicles, having a fixed part comprising an internal guide tube and a concentric external body defining a blind annular cavity suitable for being supplied with fluid and inside which there is mounted, so as to be axially movable, a piston carrying a drive element suitable for acting on the declutching device of a clutch.
2. Description of the Related Art
Such a receiver, also referred to as a hydraulic receiving cylinder, is described in the document EP-B-0 168 932.
In the latter, the internal guide tube is metallic and projects axially with respect to the external body. This tube has at its rear end a transverse plate trapped, in use, between two opposite surfaces formed respectively on the external body and on a fixed structure to which the external body is fixed.
In addition, provision is made for fixing the plate to the body by clamping, as can be seen in FIG. 1 of this document. A static sealing joint is interposed between the plate and the dorsal face of the external body. In use the pressure varies in the cavity delimiting, with the piston, a variable-volume control chamber.
In certain cases it may be desirable not to grip the plate between the fixed structure and the external body since this makes it necessary to provide a specific surface on the fixed structure.
In this case it may be thought to use solely a fixing by crimping of the plate onto the metallic external body made of castable material, for example based on aluminium.
A problem of strength of the fixing is then posed under the effect of the pressure variations occurring, in use, in the cavity, knowing that the guide tube plate forms the base of this cavity.
In order to do this it may be thought to stiffen the internal periphery of the plate, for example by means of a rim projecting axially with respect to the external periphery of the plate. This increases the cost of the guide tube.
The object of the present invention is to mitigate these drawbacks simply and economically.
The invention therefore aims to make the fixing of the guide tube to the external body more robust. Another aim of the invention is to reduce the cost of the guide tube.
According to the invention a receiver of the type indicated above, in which connection means act between the external body and the guide tube in order to fix the guide tube to the external body, is characterised in that the base of the blind cavity consist of an internal flange on the external body directed radially towards the axis of axial symmetry of the guide tube. By virtue of the invention it is not a radial plate on the guide tube but an internal flange on the external body which is subject in use to the pressure variations during the operations of disengaging and engaging the clutch.
This internal flange is more robust so that the connection means are conserved. The fixing of the guide tube to the external body is more robust, more reliable and more durable.
In addition, the guide tube is conserved because it is the external body which undergoes the pressure variations. The guide tube is less stressed so that the piston slides and therefore moves more precisely and accurately.
In one embodiment, the connection means act between the internal flange and the guide tube.
The guide tube being fixed to the internal flange therefore uses less consumption of materials since its fixing to the external body takes place closer to the axis of axial symmetry of the guide tube. The static sealing joint acting between the external body and the guide tube is also conserved since it is the internal flange and therefore the solid external body which undergoes the pressure variations. This joint is more economical since it is of smaller size than that of the prior art.
In one embodiment, the fluidtightness and fixing of the guide tube are achieved between the internal periphery of the internal flange and the external periphery of the guide tube.
By virtue of these characteristics it is possible for the guide tube to have no transverse plate and thus be purely tubular in shape. This makes it possible to reduce the costs, as well as the material consumed and the manufacturing operations. The guide tube is easier to store and handle. The static sealing joint has the smallest possible size and can be axially oblong in shape for a better seal.
In one embodiment the joint is mounted in a sealing groove which the internal flange has at its internal periphery. Naturally, the structures can be reversed, the groove being formed by pressing in the metallic tube.
The connection means can consist of a local upsetting or creeping of material of the guide tube in a connection groove in the internal flange. The connection groove can be produced at the axially oriented internal periphery, of the internal flange or in the transverse face, turned in the opposite direction to the cavity, of the internal flange. Thus the fixing is robust and reliable, the internal flange being thicker than the guide tube.
The connection groove can be merged with the sealing groove, the joint being interposed between the bottom of the groove, preferably splayed towards the guide tube, and the local upsetting of material of the guide tube. This makes it possible to reduce the number of machinings of the external body.
As a variant, the connection groove is distinct from the sealing groove and has a radially oblong shape for receiving an open ring of corrugated shape radially. The ring is retractable and radially deformable.
The guide tube has a groove opposite the connection groove for partial reception of the corrugated ring. The guide tube is connected to the external body by snapping on. By virtue of this arrangement, the guide tube can be symmetrical in shape and have, at its other end, an identical groove for receiving a circlip or spring ring limiting the axially movement of the piston with respect to the guide tube.
The two grooves are produced by upsetting material radially in the direction of the axis of axial symmetry of the guide tube. When the connection is effected at the transverse face of the internal flange, the guide tube can be immobilised axially by means of a circlip or a nut.
In the above, the material of the external body does not undergo any crimping operation. This body is therefore conserved and can thus be made from mouldable plastic material. In a variant, the flange made of mouldable plastic material can be reinforced by means of an insert, for example metallic.
It will be appreciated that the fixed structure has no need to be machined in order to offer a bearing surface for the guide tube.
The external body can have, at the rear of the internal flange, a housing for a rotating joint acting between the external body and a rotating shaft, such as the input shaft of the gearbox passing through the guide tube, which can surround the rotating joint.
It should be noted that the internal flange is easily obtained by moulding.
Because the guide tube is conserved, the piston can slide directly on the guide tube, and can carry at its front end a metallic bearing piece obtained by pressing.
The piston can be made from synthetic material such as mouldable plastic material reinforced with fibres. Preferably, this material has good slip qualities.
The bearing piece, in one embodiment, serves as a support for a axially acting elastically washer, referred to as a self-centring washer, pressing an internal radial flange on one of the ball bearing raceways in contact with a support section of the bearing piece. The bearing piece also bears the end of a sealing bellows and a preloading spring surrounded by the bellows.
The ball bearing is intended to cooperate with the declutching device and is advantageously fluidtight.
The declutching device can consist of diaphragm fingers forming means of engaging the clutch or clutch levers distinct from the clutch engagement means then consisting of coil springs or a Belleville washer acting between the cover and the declutching thrust plate. This clutch mechanism can be provided with a device for taking up wear compensating at least for the wear on the friction linings of the clutch friction member forming part of the clutch.
In a variant, the external body can consist of a large closure plate attached to the casing of a transmission box in order to close the opening of the said box through which an input shaft passes.
The closure plate has an internally hollow protuberance forming part of the fixed part of the concentric receiver of the hydraulic clutch control.
The protuberance is advantageously in a single piece with the plate and has on the inside the internal flange according to the invention.
In one embodiment, the connection means are then offset axially and radially with respect to the static joint.
In another embodiment, the guide tube has a transverse plate directed radially towards the outside and clamped in contact with the rear face of the transverse flange.
Other advantages will emerge from the following description, with regard to the accompanying drawings in which: